Page:The New International Encyclopædia 1st ed. v. 04.djvu/241

CARBON DISULPHIDE. sulphur. With the sulpliides ot" the alkali metals in aqueous solution it forms compounds analo- gous to the carbonates and called thiocarbo- uates; the formula of potassium thiocarbonate is K;CSj; that of potassium carbonate being K.COj. The thiocarbonates are used for destroy- ing vermin. Carbon disulphide is largely used as a solvent, in preparing' fats, extracting vege- table oils, etc. It may also be employed for the purpose of producing low temperatures; if evap- orated rapidly, as by passing a current of dry air through it, its temperature is reduced as low as (!0° below zero Centigrade. Owing to high re- fracting power, it is employed for scientific pur- poses in optics. ili.ed with nitric oxide its vapors give a bright bluish-white ilame which has been employed for photograjjliic purposes.

CARBONEAR, karnion-Or. A port of entry on Conception Bay, Xewfoundland, 25 miles northwest of Saint John's (Map: Xewfoundland, G 5). Population, in 1801, 4127; in lUOl, 3703.

CARBONIC-ACID GAS, or Carbon Dioxide (carbon -f- dioxide, from Ok. 51-, di-, double -- oxide). Choke-Bajip. or Fixed Air. A gaseous compound of carbon and oxygen represented by the formula CO;. It occurs in the free state as a constituent of atmospheric air, and in solu- tion in sea-water and mineral springs. It is largely evolved from fissures in the earth, espe- cially in volcanic districts; in certain localities in Java and in the neighborhood of Lake Laach, near the Rhine, the amount of carbon dioxide evolved is so great that birds .ittempting to fly across the poisonous spots drop dead. The fa- mous Dog Grotto, near Naples, is likewise filled to a certain height with carbonic-acid gas, by which dogs brought into the grotto are rendered insensible in a few seconds. The experiment is often performed, on pa.yinent of a small fee, for the amusement of travelers. The amount of car- bonic acid normally contained in atmospheric air is relatively small — 10,000 volumes of air contain about 3 volumes of carbon dioxide; or, which is the same, 10.000 parts by weight of air contain about 4.5 parts by weiglit of carbon dioxide. Animals constantly add to this by respiration ; plants, on the contrary, absorb the gas, which they transform, with the aid of light, into oxidizable food-matter. As a result, the amount of carbonic acid in the atmosphere tends to remain constant. However, the principal cause of the constancy of the composition of our atmosphere lies in the fact that the water of the ocean contains immense quantities of free carbonic acid. If the amount of the latter in the air should rise above the normal, the excess would be dissolved in the sea ; conversely, a cer- tain amount of the gas would escape from the water if the amount in the air ?hould fall below the normal. Slight variations, however, have been observed. Thus, in elev.ited places the amount of carbonic acid is usually smaller than near the level of the sea. In the vicinity of forests, too, especially in summer, the air con- tains somewhat less carbonic acid than the air in cities.

The average amount of carbonic acid produced in twenty-four hours by man is about 900 grams, the amount given out during the day being con- siderably greater than that produced during sleep. It has been recently suggested that the air in closed rooms may be continually purified and renewed by the use of sodium peroxide, a substance which has the property of absorbing carbonic acid and of giving olV an equivalent amount of pure o.xygen. Tlie total amount of free carbonic acid in nature is obviously very great. But even larger quantities, probably, exist combined in the forms of carbonates, such as chalk aiul limestone, forming part of the solid crust of the earth. For experimental purposes carbon dioxide is most easily jireparcd by the action of dilute hydrochloric acid on chijis of marble (calcium carbonate). Tlie large quanti- ties of carbonic acid employed in the arts are prepared in several different ways. Usually di- lute suli^huric acid is made to act on some porous variety of calcium carbonate, such as chalk. In the manufacture of mineral waters, magucsite or the densest varieties of dolomite are employed, as they are liable to contain a smaller amount of organic matter than other materials. The carbonic acid used in sugar-manufactories for precipitating lime is made by burning charcoal; the gas evolved from lime-kilns, or that produced by fermentation, is largely used for the same purpose. Carbonic acid is also extensively used in the manufacture of soda. The gas employed in making artificial mineral waters (q.v. ) must be carefully purified by passing it through solutions of potassium permanganate, which re- tains all organic impurities without attacking the gas itself. Carbonic acid does not support combustion ; it is, therefore, used, highly com- pressed in iron cylinders, as a fire-extinguisher. Besides the methods mentioned above, carbonic acid may be prepared by simply heating metal- lic carbonates; thus, in determining nitrogen, in organic analysis, the air is best expelled from the combustion-tube by means of carbonic acid made by heating sodium bicarbonate or mag- nesium carbonate. Pure carbon dioxide is a colorless gas about one and a half times as heavy as air: it has a feeble odor and a slightly acid taste. Owing to its high density, it does not rapidly difi'use through air, and may be poured like a liquid from one vessel into an- other. When absorbed by plants, its carbon is transformed into carbohydrates, while the whole of its oxygen is returned to the atmosi^liere. Yhen introduced into the stomach of man (say in the form of some mineral water), it has a refreshing effect, and promotes digestion. If inhaled, however, it is supposed to decomi)ose the heemoglobin of the blood and to enter into combination with the colored product of decom- position called hipmochromogen. It has been shown, nevertheless, that the animal organism is capable of adapting itself in a peculiar way to the action of carbonic acid ; birds confined within air-tight jars are capable of living in an atmosphere in which an animal introduced di- rectly from fresh air would die in a very short time. The simplest way of testing the air in a room is to introduce a burning candle : if it continues to burn quietly and with a bright flame, the air is pure and res]Hrable. The amount of carbonic acid in rooms should not exceed two grams to the cubic meter of air. Water contain- ing free carbonic acid is capable of attack- ing many substances that pure water cannot dissolve. Many rock formations have been de- stroyed by the action of such water on the carbonate of lime contained in them. Under crdi'